1. Field of the Invention
The present invention generally relates to the manufacture of electrical capacitors for use in integrated circuits and, more particularly, to a method of fabricating on chip metal to metal capacitors using planar processing techniques for applications such as on-chip decoupling capacitors.
2. Background Description
Presently, decoupling capacitors on an integrated circuit chip are fabricated by adding a thin dielectric layer between two metal layers as follows. First, with reference to FIG. 1, a lower metal (M1) 11 is deposited on an oxide layer 12 and patterned. After the M1 11 is deposited and patterned, a thick interlevel dielectric (ILD) 13 is applied. The ILD is then etched for both contact vias 14 and for the region 15 where the capacitor is to be formed. A blanket thin dielectric (TD) 16 is then deposited. Conventional photolithographic techniques are used to remove the TD from the contact via holes. In the structure shown, a tungsten stud 17 is formed in the region 15 where the capacitor is to be formed. Finally, the upper level metal (M2) is applied and patterned to form the top plate of the capacitor 18, the contact 19 to the lower plate and any other contacts to the circuits.
The primary drawback of such a capacitor structure is the trade off in thickness of the TD layer 16. Thinner layers are desirable for maximum capacitance, but thicker layers are required for yield and reliability considerations. The current process is not a robust reliable process because (a) it requires conformal deposition of a thin dielectric film into narrow gaps at high aspect ratios, (b) it is difficult to control residues and surface texture on top of the lower metal plate and on the sidewalls of the trough, and (c) the process must be integrated with the stud deposition process and its associated cleans.